Communications engineers face a number of challenges today, including finding ways to maximize the amount of information that can be communicated over the limited resources available. That is, with limited frequencies available over which to communicate radio signals, and with the amount of information that people wish to communicate growing rapidly, it is important to use the available facilities as efficiently as possible. As an example, in a typical home network system, more and more equipment is being associated with the network over which a myriad of signals are conducted.
A typical home installation of a single-cable network is shown in FIG. 1 as an illustrative example of an environment 10 in which the methods, networks, systems, and apparatuses described herein may be employed. Although a home network is illustrated as an example, it should be understood that the networks of the type to which the disclosed methods, networks, systems, and apparatuses pertain should not be regarded as being limited to home applications.
The environment 10 illustrates a home network system installation having four user applications, which may comprise, for illustration and not by way of limitation, a personal video recorder (PVR) 12, a set-top box (STB) 14, a television 15, and a WiFi router 16, in various separate locations of a house 11. The PVR 12 may supply recorded video and audio signals to a television 13. The set-top box 14 may supply interactive television content to a television 17. The television 15 may receive the input signals directly. The WiFi router 16 may supply digital data signals for wireless detection by a computer 18, or the like. The particular applications may be selected from a myriad of other functional apparatuses or systems. For example, apparatuses, systems, and computer program products described herein may provide a PVR system having multiple inputs, a satellite radio system, a network hub to a wireless network, such as an IEEE 802.11b Direct Sequence network, or other device that converts radio-frequency signals to a useful user form, or the like.
It should also be noted that although a single dwelling or house 11 is shown for purposes of illustration, the methods, circuits, devices, apparatuses, and systems described herein may be employed in a myriad of other installation locations. One example may include an apartment complex in which signals may be deployed to a number of buildings to which signals received on a single-cable may be used. Another example may include a business building in which signals may be deployed to a number of offices to which signals received on a single-cable may be used. Other examples are manifold.
Intermediate frequency (IF) signals are sourced from, for example, an external plant, such as a cable television (CATV) signal source, a satellite signal source, or the like, on a coaxial cable 30. In some cases, a fiber optic cable is used in the external plant (e.g., a fiber optic service like “FiOS”, provided by Verizon Communications). In such cases, the fiber is terminated in a unit that converts signals from optical domain to electrical and vice versa (such as an Optical Network Terminal (ONT) used in the FiOS system). Such a unit is inserted between the outdoor fiber optic cable and the indoor coaxial cable. The unit may be installed on the outside or the inside of the home, in front of the top splitter 24 in FIG. 1. The signals to the personal video recorder (PVR) 12, set-top box (STB) 14, television 15, and WiFi router 16 may be delivered on coaxial cables 20, 27, 29, 31, 21, and 22 via signal dividers or splitters 24, 25, and 26. In the embodiment shown, the splitter 24 is a top-level splitter that receives the signals from the external coax plant on a single cable 30, and the splitters 25 and 26 are lower level splitters. The lower level splitter 25 splits the signals from one of the outputs of the top-level splitter 24 from a cable 31 to provide the signals to cables 21 and 22. The lower level splitter 26 splits the signals from one of the outputs of the top-level splitter 24 from the cable 20 to provide the signals to cables 27 and 29.
The splitters 24, 25, and 26 are shown in FIG. 1 as being two-way splitters. However, the splitters may of any type that splits an input signal into a number of output signals, 2-, 4-, and 8-way splitters being typically employed. Sometimes splitters with non-binary number of outputs may be used, such as 6-way, or even with an odd-number of outputs, e.g. a 3-way splitter. The splitters 24, 25, and 26 are of the type that allows bi-directional passage of RF and DC signals. Thus, the splitters may feed a signal having combined user bands (UBs) to the personal video recorder (PVR) 12, set-top box (STB) 14, television 15, and WiFi router 16 in one direction. The splitters also may provide for passage of command signals (for example DiSEqC™ signals of the type described by the CENELEC EN 50494 standard command structure) between the, personal video recorder (PVR), set-top box (STB) 14, television 15, and WiFi router 16 and the ODU 28 in the other direction.
The cables 30, 31, 20, 21, 22, 27 and 29 may be of any suitable cable construction, such as a coaxial cable, plastic optical fiber (POF), or the like. It should be noted that in a single-cable network, even though there are physically different cables, for example, cables 30, 31, 20, 21, 22, 27 and 29 each carries same information, effectively providing a single-cable network. The network itself may be constructed to operate using a MoCA protocol, for example, as defined by the Multimedia over Coax Alliance. Under the MoCA protocol, each device that is connected to the network can communicate with any other device that is also connected to the network.
An abstracted high-level block diagram of the cable distribution system 50 in a network system of the type illustrated in FIG. 1 is shown in FIG. 2, to which reference is now additionally made. The cable distribution system 50 includes a top-level splitter 24, which may correspond to the top-level splitter 24 in the system 10 of FIG. 1. The top-level splitter 24 receives an input signal on line 32 from a point of entry 51 to which signals to and from the external coax plant are connected via coaxial cable 30.
The top-level splitter 24 may be an N-way splitter (additional outputs being provided in contrast to the splitter embodiment of FIG. 1), splitting the input signal on line 30 to provide the signal to n output lines 20, 31, and 52 . . . 54. The coaxial cable lines 20 and 31 correspond, for example, to the coaxial cable lines 20 and 31 shown in FIG. 1. The signals on output line 20 may be further split by a lower-level Q-way splitter 26, and the signals on output line 31 may be further split by a lower-level P-way splitter 25. (Again, each splitter is shown with additional outputs in contrast to the splitter embodiments of FIG. 1.) Although the N-way splitter 24, Q-way splitter 26, and P-way splitter 25 are labeled as possibly having a different number of outputs, N, P, and Q may be the same. The signals on the output lines 52 . . . 54 may be further split by additional lower-level splitters, not shown. The outputs from the splitters 25 and 26 and the splitters, not shown, on lines 52 and 54 may be connected to various user devices in known manner. The P and Q are integer numbers having a value in the range of 2 through 32 or higher.
For illustration, one of the outputs of the Q-way splitter 26 is connected to an outlet A in communication with the communication device #1 64. In like manner, one of the outputs of P-way splitter 25 is connected to an outlet B in communication with the communication device #2. Another of the outputs of the P-way splitter 25 is connected to an outlet M in communication with the communication device #M 68. Although not shown, it should be understood that the network 50 may include additional lower level splitters, if desired, that receive output signals from one or more lower level splitters 25, . . . , 26.
In operation, signals from the point of entry 51 are split by the various splitters in the network, ultimately to be delivered to any device on any node in the network. For example, in the embodiment illustrated, the signals at the point of entry 51 are delivered via outlet A to communication device #1 64, via outlet B to communication device #2 66, via outlet M to communication device #M 68, and to any other device, not shown, connected to a splitter output. In addition, with the network being operated in accordance with a MoCA protocol, any device, itself, can communicate with any other device in the network. Thus, for example, communication device #2 66 can communicate with communication device #M 68 along a communication channel comprising only the lower level splitter 25. Alternatively, communication device #1 64 can communicate with communication device #2 66 from outlet A, along a communication channel comprising the lower lever splitter 26, up to the top-level splitter 24, and back down through the lower level splitter 25 through outlet B.
With regard to the construction of the splitters typically used in community antenna television (CATV) home coaxial cable networks, such splitters are typically designed to pass signals up to about 1 GHz in the direction from the point of entry (POE) 51 to the various outlets, such as outlet A, outlet B, . . . , and outlet M. Since splitters are passive devices, they can also pass signals in a reverse direction up to about 1 GHz in a direction from the various outlets to the point of entry (POE) 51. Above 1 GHz, for example, between 1.1 GHz and 1.7 GHz, however, the splitter losses are higher. In the majority of cases (majority of outlets/homes), a total path loss from outlet to outlet in the 1.1 GHz to 1.7 GHz band may be less than 65 dB. This includes cable losses, in-out or out-in splitter losses, and losses due to splitter isolation. (The terms “splitter isolation” or “isolation losses” refer to path losses in the splitter from one splitter output to another output of the same splitter that must be traversed or “jumped” by the signal traveling from one network node to another through the splitter. Only one such “jump” is needed across any particular splitter to close the signal path.) With 65 dB of loss, using a channel bandwidth of about 200 MHz, a throughput of close to 1 Gigabits/second (Gbps) can be achieved, for example, in a MoCA 2.0 networking system. The loss characteristics of home coaxial cable systems in the frequency range above about 2 GHz, however, is generally considered excessively lossy, and, as such, this frequency range is unsuitable or unusable for communications. Moreover, to achieve data rates on the order of 10 Gbps and above, the bandwidth available in this frequency range is not sufficient in present-day networks.
Thus, in a frequency range above 2 GHz, up to 10 GHz or more, a bandwidth of 8 GHz, or more, is unusable in today's home coaxial cable networks, due to the very high path loss from outlet to outlet at these frequencies. An analysis of home systems shows that the outlet-to-outlet loss in 2-10 GHz range can be up to 90 dB in a vast majority of cases. This 90 dB signal loss is excessive, and limits the achievable communications rate because the received signal-to-noise ratio (SNR) is low, even assuming a transmitter power of +10 dBm and a receiver noise figure of 5 dB (i.e., levels that are typical of the current state of the art RF front-end technology for consumer products). According to Shannon's channel capacity theory, in this case the channel capacity is limited to about 1 Gbps, even if an 8 GHz bandwidth is used. That is, under these conditions, increasing the channel bandwidth cannot increase the channel capacity above 1 Gbps. This is illustrated in the graph in FIG. 3, which shows a plot of channel bandwidth in GHz vs. maximum transmission rate in Gbps for a 90 dB path loss, assuming the above stated transmission and reception characteristics. It can be seen that the curve 70 is essentially flat, indicating that increasing the channel bandwidth does not result in an increase in the maximum transmission rate that can be achieved.
What is needed are methods, circuits, devices, apparatuses, and systems that can be used in coaxial cable networks of the type described that can achieve an increased channel capacity.